Stoker-fired, coal-burning heater



M r h 1967 J. L. MARGETTS STOKER-FIRED,

COAL-BURNING HEATER 2 Sheets-Sheet 1 Filed July 6, 1965 INVENTOR. JOHN L. MARGETTS ATTORNEYS United States Patent 3,311,074 STQKER-FIRED, COAL-BURNING HEATER J ohu L. Margetts, 2182 Berkley Ave., Salt Lake City, Utah 84109 Filed July 6, 1965, Set. No. 469,813 6 Claims. (Cl. 110-45) This invention relates to small, domestic, Stoker-fired, coal-burning heaters of the type shown in my US. Patent No. 3,149,625, granted Sept. 22, 1964 and entitled, Power Stoked, Coal-Fired Heating Unit.

It has now been found desirable to produce such heaters with even smaller heating capacity than originally contemplated, for example, with a capacity of approximately 40,000 B.t.u. per hour as compared with 85,000 B.t.u. per hour. This has posed problems, in that the use of a conventional feedscrew large enough to supply required amounts of coal to the firebox Without exerting a crushing action on the coal requires such slow feeding of a large mass of coal that the fire can easily burn back through the feed assembly into the hopper.

If the feedscrew and tube in which it operates are simply made smaller in diameter, to decrease the mass of coal fed per unit time so the feed rate can be increased sufficiently to prevent back burning, the coal is subjected to crushing action between the solid core of the screw and the tube. This necessitates an excessively large power source. Moreover, crushing of the coal tends to compact it in the feed tube and to thereby not only increase frictional resistance to its movement, but to also require higher pressure for the combustion air forced into the fuel bed. As a practical matter, these problems have heretofore made it impossible to produce a stoker-fired, coal-burning heater of unusually low heat output for very small homes and other enclosures.

The principal object of the present invention is to provide a construction for stoker-fired, coal-burning heaters of the type concerned that will enable coal to be efficiently burned .at an exceptionally slow rate without the problems mentioned above.

Although the present invention makes production of such a heater both possible and practical, its benefits are not restricted to heaters of excessively small size but can be also applied with advantage to larger capacity heaters of the type concerned.

In accordance with the invention, a special spiral shaped feed member, differing from the usual feedscrew in that it has no central core and in that is has heavy bar-like convolutions for structural strength in the small diameters involved, is used to move coal from a hopper to a firebowl. The continuous open spaces between the heavy bar-like convolutions provide pockets through which coal is pushed without being crushed. It is therefore possible to feed relatively small quantities of coal through a small diameter tube at a rate sufficient to prevent burning back of the coal from firebowl to hopper and to do this by means of a relatively small electric motor. Moreover, a single, relatively small fan can be used to both cool the motor and provide the air necessary for efficient combustion.

There is shown in the accompanying drawings a specific embodiment of the invention representing what is presently regarded as the best mode of carrying out the generic concepts in actual practice. From the detailed description of this presently preferred form of the invention, other more specific objects and features will become apparent.

In the drawings:

FIG. 1 is a view in side elevation of a heater conforming to the invention, portions being broken away to show internal operating mechanism and the feed tube being "ice shown in axial longitudinal section to reveal the helical feed member in side elevation;

FIG. 2, a fragmentary vertical section taken on the line 22 of FIG. 1 and drawn to a somewhat larger scale;

FIG. 3, a fragmentary horizontal section on the line 3-3 of FIG. 2 and drawn to the same scale as FIG. 2;

FIG. 4, a fragmentary vertical section taken on the line 4-4 of FIG. 1 and drawn to the same scale as FIGS. 2 and 3, hidden parts being shown by dotted lines;

FIG. 5, a fragmentary elevational view taken on the line 55 of FIG. 1 and drawn to the same scale as FIGS. 2, 3, and 4; and

FIG. 6, a perspective view of the fan housing taken from the right of FIG. 5 and in vertical section at the rear of such housing.

Referring now to the drawings:

In the illustrated embodiment the heater 10, FIG. 1, includes an exterior housing 11 of simple box-like configuration compartmented by internal walls 12, 13, and 14 to provide a coal hopper 15 and separate compartments for operating components. A heat exchanger 16 is positioned in one of the compartments above a firebowl 17. A door 18 in the top of housing 11 opens into hopper 15 for the introduction of coal, which feeds into a Well 19 and into a helical feed member 20 which takes the place of the usual feedscrew.

Feed member 20 operates in a tube 21, which leads into the bottom of firebowl 17 in the usual manner. It is turned by a small electric motor 22 positioned within a' fan housing 23 that is located in another compartment of housing 11 beneath sloping wall 13.

Unlike the usual feed mechanisms employing feedscrews having a helical flight wrapped about an elongate shaft forming a solid core, there is no solid core in the feed member or feedscrew 20. A helical flight alone, formed of heavy bar stock or cast to formation preferably polygonal in cross section, provides an open helix through whose open center 20a and between whose convolutions 20b the coal is moved. Passage for pieces of coal of slack size is provided without crushing action, even though the internal diameter of the tube and external diameter of the helix are unusually small, e.g., approximately one and a quarter inches. Thus, the torque required to turn the feed member is low.

In practice, it has been found that the illustrated rectangular cross section of the convolutions is best adapted to move coal through the tube, and, at the same time provides necessary structural strength. The spaces between convolutions can easily be made wide enough to accommodate pieces of coal up to 1% inches in diameter, as ordinarily required by reason of the fact that most slack coal is screened through a l A-inch screen.

Utilizing the feed mechanism of the invention, it has been possible to maintain the necessary rate of feed of coal to the firebowl to prevent bum-back, without supplying more coal than will produce the limited amount of heat desired. For example, with a tube having a two inch inside diameter and a helix feed member having convolutions of one-half inch by one-half inch bar stock steel, the spaces between the convolutions being slightly more than 1% inches across, it has been possible to feed as little as three pounds of coal per hour or as much as six pounds of coal per hour to the firebowl, the amount depending on the speed of rotation of the feed member. This has maintained the fire in the firebowl without burn-back.

Since the torque required to turn helix 20 is low, the small electric motor 22 can be used both as a power source therefor, operating through reduction gearing in a gear box 24, and to provide power for operating a fan 25, of preferably bladed centrifugal type as illustrated,

to supply forced draft to firebox 17 for combustion of the coal fed thereto. The fan and gear box are advantageously positioned, along with motor 22, in fan housing .23.- As illustrated, motor 22 is fixed to posts 26- and 27 that extend outwardly from the gear box.

Airsucked into housing 23 through openings 11a of housing ll and intake opening 23a of the fan housing by fan 25 operating with respect to a preferably involute baffie 28 inside the housing is first directed against electric motor, 22 to keep it cool and then into a pair of ducts 1 39 is regulated by dampers 34 and 35, respectively, which can be set to cover any desired portion of their respective duct openings merely by sliding their respective slideway slots 36 with respect to guide pins 37, FIGS. 35, that are fixed to a plate 38.

As illustrated, fan housing 23 is removably fixed to plate.38 by ears 39 that are positioned over studs 40 and held in place by nuts 41. Gear box 24 is also fixed to plate 38 with screws 42, FIG. 4, or other conventional anchoring arrangement, and the plate 38 is fixed to wall 14 by bolts 43 and nuts 44.

A screen 45 is positioned to cover the opening 23a of the fan housing to prevent entrance of undesired foreign matter into the fan blades 24a.

Whereas there is here illustrated and specifically described a certain preferred construction of apparatus which is presently regarded as the best mode of carrying out the invention, it should be understood that various changes may be made and other constructions adopted without departing from the inventive subject matter particularly pointed out and claimed herebelow.

I claim:

1.; A stoker-fired,coal-burning heater, comprising a housing;

partition walls within said housing defining a hopper for coal to be burned;

a firebowl within said housing remote from the hopa coal feed tube extending from the hopper to the firebowl:

feed means for moving coal through said tube from the hopper to the firebowl;

a motor;

drive means connecting the motor with the said feed means, whereby said motor operates said feed means;

a fan, driven by the motor;

duct means for carrying air from the fan to the firebowl; and

means arranging the fan to discharge air against the motor before passage into the duct means.

2. A stoker-fired, coal-burning heater according to claim 1, wherein the feed means comprises a bar of helical shape and having an open central passage forming a longitudinal axis therethrough.

3. A stoker-fired, coal-burning heating unit according to claim 2, further including a fan housing communicating at one end with the duct means, the motor being mounted within the fan housing intermediate its length and the fan being mounted within the fan housing at its other end; and a bafile positioned within the fan housing to direct air from the fan toward the motor and duct means.

4. A stoker-fired, coal-burning heater according to claim 3, wherein the fan is of bladed centrifugal type and the bafiie is of involute formation.

5. A stoker-fired, coal-burning heater according to claim 3, wherein the firebowl includes tuyere structure for supplying primary combustion air; wherein there is additionally provided overhead jet means for supplying secondary air to the firebowl; and wherein the duct means includes a duct communicating with said jet means and a duct communicating with said tuyere structure.

6. A stoker-fired, coal-burning heater according to claim 2, wherein the inside diameter of the feed tube and the outside diameter of the feed means are of the magnitude of approximately one and a quarter inches.

References Cited by the Examiner UNITED STATES PATENTS 459,518 9/1891 Brown -45 1,206,071 11/1916 Wood 1l044 1,880,840 10/1932 Currier 110-44 2,141,831 12/1938 Stockstrom 110-110 2,170,277 8/1939 Richardson 11045 2,378,376 6/1945 Ackron 110-45 2,507,245 5/1950 Dady 1l0-45 KENNETH W. SPRAGUE, Primary Examiner. 

1. A STOKER-FIRED, COAL-BURNING HEATER, COMPRISING A HOUSING; PARTITION WALLS WITHIN SAID HOUSING DEFINING A HOPPER FOR COAL TO BE BURNED; A FIREBOWL WITHIN SAID HOUSING REMOTE FROM THE HOPPER; A COAL FEED TUBE EXTENDING FROM THE HOPPER TO THE FIREBOWL: FEED MEANS FOR MOVING COAL THROUGH SAID TUBE FROM THE HOPPER TO THE FIREBOWL; A MOTOR; DRIVE MEANS CONNECTING THE MOTOR WITH THE SAID FEED MEANS, WHEREBY SAID MOTOR OPERATES SAID FEED MEANS; A FAN, DRIVEN BY THE MOTOR; DUCT MEANS FOR CARRYING AIR FROM THE FAN TO THE FIREBOWL; AND MEANS ARRANGING THE FAN TO DISCHARGE AIR AGAINST THE MOTOR BEFORE PASSAGE INTO THE DUCT MEANS. 